Solar substrate ribbon bonding system

ABSTRACT

An ultrasonic solar substrate bonding system is provided. The system includes a bond head assembly including a bonding tool for bonding a ribbon material to a plurality of solar substrates. The system also includes a ribbon feeding system successively supplying portions of a continuous length of the ribbon material to the bonding tool such that the bonding tool forms ultrasonic bonds between the portions of the continuous length of the ribbon material and a plurality of solar substrates.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/389,022, filed Oct. 1, 2010, the contents of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to ultrasonic bonding operations, and moreparticularly, to ultrasonic ribbon bonding systems for solar cells andthe like.

BACKGROUND OF THE INVENTION

In the processing and packaging of semiconductor devices, ultrasonicbonding (e.g., wire bonding, ribbon bonding, etc.) continues to be awidely used method of providing electrical interconnection between twolocations within a package (e.g., between a bond pad of a semiconductordie and a lead of a leadframe). For example, ribbon bonding machines areused to form ribbon interconnections between respective locations to beelectrically interconnected. The upper terminal end of a bonding toolis, in many instances, configured to be engaged in a transducer (e.g.,an ultrasonic transducer) of a ribbon bonding system which causes thebonding tool to vibrate upon bonding. Ultrasonic bonding is a joiningprocess that, for example, may use relative motion between the ribbonand the surface it is bonded to. It is this relative motion that enablesthe bond formation.

In providing interconnection in solar cell applications (e.g.,crystalline silicon solar cells, thin film solar cells, etc.),techniques such as soldering or conductive adhesive bonding have beenused to electrically connect adjacent cells, to collect electricity frommultiple cells, etc.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, anultrasonic solar substrate bonding system is provided. The systemincludes a bond head assembly including a bonding tool for bonding aribbon material to a plurality of solar substrates. The system alsoincludes a ribbon feeding system successively supplying portions of acontinuous length of the ribbon material to the bonding tool such thatthe bonding tool forms ultrasonic bonds between the portions of thecontinuous length of the ribbon material and a plurality of solarsubstrates.

According to another exemplary embodiment of the present invention, amethod of providing electrical interconnection between solar substratesis provided. The method includes the steps of: (1) providing a bond headassembly including a bonding tool; (2) ultrasonically bonding a portionof a ribbon material to a bonding location of a first solar substratewith the bonding tool to form a first bonded portion; (3) extending alength of the ribbon material continuous with the first bonded portionto a second solar substrate; and (4) ultrasonically bonding anotherportion of the ribbon material, continuous with the length of the ribbonmaterial, to a bonding location of the second solar substrate with thebonding tool to form a second bonded portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following figures:

FIG. 1 is a plan overhead block diagram view of an ultrasonic solarsubstrate bonding system in accordance with an exemplary embodiment ofthe present invention;

FIGS. 2A-2L are a series of plan overhead block diagram views of theultrasonic solar substrate bonding system of FIG. 1, illustrating asequential ribbon bonding operation in accordance with an exemplaryembodiment of the present invention;

FIGS. 3A-3D are a series of plan overhead block diagram views of anotherultrasonic solar substrate bonding system illustrating a sequentialribbon bonding operation in accordance with another exemplary embodimentof the present invention;

FIGS. 4A-4D are a series of plan overhead block diagram views of yetanother ultrasonic solar substrate bonding system illustrating asequential ribbon bonding operation in accordance with yet anotherexemplary embodiment of the present invention;

FIGS. 5A-5D are a series of plan overhead block diagram views of yetanother ultrasonic solar substrate bonding system illustrating asequential ribbon bonding operation in accordance with yet anotherexemplary embodiment of the present invention;

FIGS. 6A-6C are a series of plan overhead block diagram views of yetanother ultrasonic solar substrate bonding system illustrating asequential ribbon bonding operation in accordance with yet anotherexemplary embodiment of the present invention;

FIG. 7 is an overhead and cross sectional block diagram view of portionsof a material handling system in accordance with an exemplary embodimentof the present invention; and

FIGS. 8A-8F are a series of overhead block diagram views, andcorresponding cross-sectional side block diagram views, of a materialhandling system of an ultrasonic solar substrate bonding system inaccordance with yet another exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates ultrasonic ribbon bonding system 100 (e.g., anultrasonic solar substrate bonding system) for bonding conductive ribbonmaterial (not shown) between solar substrates (with only one solarsubstrate “A” visible in FIG. 1) (e.g., crystalline solar cells, thinfilm solar cells, etc.). Ultrasonic bonding system 100 includes inputstack 102 of solar substrates, with first solar substrate “A” shown onthe top of input stack 102. To the right of input stack 102 is alignmentunit 104 (e.g., a centering unit) which includes camera 106 (e.g., alook-up camera as shown, a downward looking camera, etc.). Alignmentunit 104 may include a material handling system for supporting andtransporting ones of a plurality of solar substrates. Material handlingcomponents are known to those skilled in the art and include grippingmechanisms, pushing mechanisms, pulling mechanisms, lifting mechanisms,flipping mechanisms, etc. (none shown), as is desired in the givenapplication, and may be configured to position ones of the plurality ofsolar substrates in a predetermined position prior to bonding by thebonding tool. Camera 106 may be configured for imaging ones of theplurality of solar substrates prior to bonding by the bonding tool,where such images may be used by alignment unit 104 in positioning onesof the plurality of solar substrates in a predetermined position.

Ultrasonic bonding system 100 also includes indexing system 108 (alsoknown as a material handling system) for holding and moving a pluralityof solar substrates “A”, “B”, “C”, etc. In the illustrated example, thematerial handling system comprises walking beam structure 110 configuredto move ones of the plurality of solar substrates with respect to a bondhead assembly, and a workholder structure configured to support ones ofthe plurality of solar substrates during a ribbon bonding operation(e.g., see FIGS. 7 and 8 a). In the illustrated example, indexing system108 includes string walking beam 110 (the operation of which isdescribed below); however, other types of indexing systems arecontemplated. The material handling system may be configured to: (1)support ones of the plurality of solar substrates upstream of the bondhead assembly; (2) position ones of the plurality of solar substratesunder the bond head assembly for bonding by the bond head assembly; and(3) support bonded ones of the plurality of solar substrates downstreamof the bond head assembly.

Ribbon bonder 112 is provided along the length of indexing system 108.Ribbon bonder 112 includes XY table 114 for carrying a bond headassembly. The bond head assembly (not shown in FIG. 1) includes elementsdesired in the given application such as a transducer, a ribbon bondingtool, etc. The operation of the exemplary system shown in FIG. 1 is nowdescribed in connection with FIGS. 2A-2L.

FIG. 2A illustrates solar substrates “A”-“E” that have been moved frominput stack 102 to indexing system 108 (using alignment unit 104), withanother solar substrate “F” on the top of input stack 102. In thisexample, it is desired to electrically interconnect each of substrates“A”-“E”. In FIG. 2A solar substrate “A” is being bonded by ribbon bonder112 after substrate “A” has been placed in a bonding position on ribbonbonder 112. That is, ribbon material 116 is being continuously fed froma ribbon feeding system (not shown) that is carried by XY table 114, andis being bonded to solar substrate “A”. For example, ribbon material 116may be bonded to the bottom of solar substrate “A” to, for example,allow the active solar material on the top of solar substrate “A” to befree of ribbon material 116 which would tend to block absorption ofsolar energy by the solar substrate's active material. Of course, theteachings of the present invention may also be applied to bonding ribbonmaterial 116 to a portion (e.g., a conductive busbar or the like) on thetop side of solar substrate “A” (or both the top and bottom ofsubstrates).

FIG. 2A illustrates ‘lower’ portion 118 of ribbon material 116 beingbonded (actively being bonded) to substrate “A” (e.g., using a ribbonbonding tool, not shown in FIG. 2A). In FIG. 2B, another portion 118 isbeing bonded, while the portion 118 that was being bonded in FIG. 2A isnow bonded portion 118 a. For example, XY table 114 has moved betweenFIG. 2A and FIG. 2B so that another portion 118 may be bonded in FIG.2B. In FIG. 2C, three bonded portions 118 a, 118 b, 118 c have now beencompleted (but could be any number of bonded portions) on solarsubstrate “A”, and now it is time to continue bonding the ribbonmaterial (e.g., in a continuous length) to next solar substrate “B”.Indexing system 108 (e.g., string walking beam 110) is used to movesolar substrates “A”-“E” so that solar substrate “B” is positioned inthe bonding position on ribbon bonder 112 (i.e., the position shown inFIG. 2D). FIG. 2D also illustrates three bonded portions 118 d, 118 e,118 f having been formed on solar substrate “B”. The process of indexingand bonding solar substrates “C”, “D”, “E” continues, and FIG. 2Eillustrates three bonded portions 118 g, 118 h, 118 i on solar substrate“C”, FIG. 2F illustrates three bonded portions 118 j, 118 k, 118 l onsolar substrate “D”, and FIG. 2G illustrates three bonded portions 118m, 118 n, 118 o on solar substrate “E”. At this point (at FIG. 2G) acontinuous length of ribbon material 116 has been bonded across stringof solar substrates “A”-“E” (e.g., where the string includes five solarsubstrates “A”, “B”, “C”, “D”, “E” in this example, but may include anynumber of substrates), and bonded length of ribbon material 116 isseparated from a ribbon supply (e.g., using a cutter, etc.—not shown)past bonded portion 118 o.

In this example, it is now desired to bond another ‘upper’ continuouslength of ribbon material 116′ across solar substrates “A”-“E”, forexample, spaced apart from, and in a substantially parallel orientationto, bonded ribbon material 116, as will now be described in connectionwith FIGS. 2H-2L. Thus, indexing system 108 is used to move solarsubstrates “A” through “E” such that solar substrate “A” is back in thebonding position on ribbon bonder 112. In FIG. 2H another bonded portion118′a has been formed on second continuous length of ribbon material116′ on solar substrate “A”. At FIG. 2I, three bonded portions 118′a,118′b, 118′c have been completed on solar substrate “A”. The process ofindexing (and bonding) now continues such that at FIG. 2J three bondedportions 118′a-118′c; 118′d-118′f; 118′g-118′i′; 118′j-118 l have beenformed on each of respective solar substrates “A”-“D”, and portion 118′is being bonded on solar substrate “E”. At FIG. 2K, three bondedportions 118′m, 118′n, 118′o have been formed between second length ofribbon material 116′ and solar substrate “E”. Second continuous lengthof ribbon material 116′ is then separated from the ribbon supply (e.g.,using a cutter, etc.), and string of bonded solar substrates “A”-“E” isindexed to the right in FIG. 2L, clear of the bonding position on ribbonbonder 112, to await further processing. Thus, in FIGS. 2A-2L, anexemplary system and method is shown that is configured to bond multiplecontinuous lengths of ribbon material to a string of adjacent solarsubstrates using a single ribbon bonder.

FIGS. 3A-3D illustrate an exemplary system configured to bond multiplecontinuous lengths of ribbon material 316, 316′ to a string of solarsubstrates “A”-“E” using two ribbon bonders 312, 312′, wherein ribbonbonders 312, 312′ are provided on opposite sides of indexing system 308.The other components of ultrasonic solar substrate bonding system 300 inFIGS. 3A-3D may be substantially similar to those illustrated anddescribed with respect to FIGS. 2A-2L and using a different number ofsolar substrates but still identified as solar substrates “A”, “B”, “C”,etc.

At FIG. 3A, solar substrate “A” is in the bonding position for both ofribbon bonders 312, 312′, with solar substrate “B” downstream of ribbonbonders 312, 312′ (where ribbon bonders 312, 312′ are represented by asingle dashed box), and solar substrate “C” on input stack 302. Firstribbon bonder 312′ has formed three bonded portions 318′a, 318′b, 318′c(on upper continuous length of ribbon material 316′) on solar substrate“A”, and second ribbon bonder 312 has formed three bonded portions 318a, 318 b, 318 c (on lower continuous length of ribbon material 316) onsolar substrate “A”. The process of indexing and bonding continues suchthat at FIG. 3B, first ribbon bonder 312′ has formed three bondedportions 318′d, 318′e, 318′f (on upper continuous length of ribbonmaterial 316′) on solar substrate “B”, and second ribbon bonder 312 hasformed three bonded portions 318 d, 318 e, 318 f (on lower continuouslength of ribbon material 316) on solar substrate “B”. The process ofindexing and bonding continues on such that at FIG. 3C, the twocontinuous lengths of ribbon material 316, 316′ have been bonded acrosseach of solar substrates “A”-“E”, and, each of upper and lowercontinuous lengths of ribbon material 316′, 316 have been separated fromtheir respective ribbon supplies (e.g., using a cutter, etc.). At FIG.3D, the string of bonded solar substrates “A”-“E” has been indexed tothe right, clear of the bonding position on ribbon bonders 312, 312′, toawait further processing.

FIGS. 4A-4D illustrate an exemplary process similar to that in FIGS.3A-3D except that first ribbon bonder 412 and second ribbon bonder 412′are positioned adjacent one another on one side of indexing system 408(and not opposing one another as in FIGS. 3A-3D) (where ribbon bonders412, 412′ are represented by a single dashed box). The other componentsof the system in FIGS. 4A-4D may be substantially similar to thoseillustrated and described with respect to FIGS. 2A-2L and FIGS. 3A-3D.In a bonding operation before FIG. 4A (not shown), first ribbon bonder412 (including XY table 414) has formed three bonded portions 418 a, 418b, 418 c between lower continuous length of ribbon material 416 andsolar substrate “A”. Then solar substrate “A” has been indexed to aposition to be bonded by second bonder 412′ (as shown in FIG. 4A), andsolar substrate “B” has been indexed to a position to be bonded by firstbonder 412 (as shown in FIG. 4A). In FIG. 4A, second ribbon bonder 412′has formed three bonded portions 418′a, 418′b, 418′c between uppercontinuous length of ribbon material 416′ and solar substrate “A”, andfirst ribbon bonder 412 has formed three bonded portions 418 d, 418 e,418 f between lower continuous length of ribbon material 416 and solarsubstrate “B”, with solar substrate “C” on the top of input stack 402 tothe left of camera 406 of alignment unit 404.

The process of indexing and bonding continues such that at FIG. 4B,second ribbon bonder 412′ has formed three bonded portions 418′d, 418′e,418′f between upper continuous length of ribbon material 416′ and solarsubstrate “B”, and first ribbon bonder 412 has formed three bondedportions 418 g, 418 h, 418 i between lower continuous length of ribbonmaterial 416 and solar substrate “C”. This process of indexing andbonding continues such that at FIG. 4C, two continuous lengths of ribbonmaterial 416, 416′ have been bonded across each of solar substrates“A”-“E”, where each of continuous lengths of ribbon material 416, 416′has been separated from its respective ribbon supply (e.g., using acutter, etc.). As will be appreciated by one skilled in the art, lowercontinuous length of ribbon material 416 may be (if desired) separatedfrom its ribbon supply prior to solar substrate “E” being indexed to thebonding position of second ribbon bonder 412′. At FIG. 4D, string ofbonded solar substrates “A”-“E” has been indexed to the right, clear ofthe bonding position of second ribbon bonder 412′, to await furtherprocessing.

Each of the exemplary embodiments of FIGS. 2A-2L, FIGS. 3A-3D, and FIGS.4A-4D illustrate bonding continuous lengths of ribbon material betweenadjacent solar substrates. FIGS. 5A-5D illustrate bonding multiple,respective, separate lengths of ribbon material between adjacent solarsubstrates. The other components of the system in FIGS. 5A-5D may besubstantially similar to those illustrated and described with respectto, for example, FIGS. 2A-2L (including corresponding elements inputstack 502, camera 506, alignment unit 504, XY table 514, etc.). At FIG.5A, single lower separate length of ribbon material 520 a is bondedbetween solar substrate “A” and solar substrate “B” with separate lengthof ribbon material 520 a having been separated from the ribbon supply(not shown). The process of indexing and bonding continues such that atFIG. 5B additional individual lower separate lengths of ribbon material520 b, 520 c, 520 d have been bonded between respective adjacent ones ofsolar substrates “B”-“C”, solar substrates “C”-“D”, and solar substrates“D”-“E”.

At FIG. 5C, a single upper separate length of ribbon material 520′a, isbonded between solar substrate “A” and solar substrate “B”, with upperseparate length of ribbon 520′a having been separated from the ribbonsupply (not shown). The process of indexing and bonding continues suchthat at FIG. 5D additional individual upper separate lengths of ribbonmaterial 520′b, 520′c, 520′d have been bonded between respectiveadjacent ones of solar substrates “B”-“C”, “C”-“D”, and “D”-“E”, andwith the bonded string of solar substrates “A”-“E” having been furtherindexed to the right, clear of the bonding position on ribbon bonder512, and awaiting further processing.

In each of FIGS. 2A-2L, FIGS. 3A-3D, FIGS. 4A-4D, and FIGS. 5A-5D twolengths of ribbon material (continuous lengths in FIGS. 2A-2L, FIGS.3A-3D, and FIGS. 4A-4D, and non-continuous or separate, lengths (fromone or more continuous supplies of ribbon material) in FIGS. 5A-5D) areprovided between each of the adjacent solar substrates. Of course, anynumber of lengths (e.g., one length, three lengths, etc.) of ribbonmaterial (and any number of ribbon bonders, if it is desired to have onebonder for each length of ribbon as in FIGS. 3A-3D and FIGS. 4A-4D) maybe provided as is desired in a given application.

FIGS. 6A-6C illustrate single continuous length of ribbon material 616being bonded between solar substrates “A”-“E” using ultrasonic solarsubstrate bonding system 600. The components of the system in FIGS.6A-6C (and the process of indexing and bonding) may be substantiallysimilar to those illustrated and described above with respect to, forexample, FIGS. 2A-2L (including corresponding elements input stack 602,camera 606, alignment unit 604, XY table 614, etc.). For example,substrate “A” is aligned with, and positioned at, the bonding positionfor ribbon bonder 612 and ribbon material 616 is bonded to substrate “A”substantially along the midpoint of substrate “A” between its upper andlower horizontal edges by bonds 618 a, 618 b, 618 c. String of solarcells “A”-“E”, for example, are indexed such that substrate “B” ispositioned at the bonding position for ribbon bonder 612 and three bonds618 d, 618 e, 618 f are formed between continuous ribbon material 616and substrate “B”. Substrates “C”-“E” are also, in turn, so bonded suchthat continuous length of ribbon material 616 is bonded to each. Asillustrated in FIG. 6C, continuous length of ribbon material 616 wassevered from its ribbon supply, and bonded substrates “A”-“E” wereindexed by index system 608 to be clear from ribbon bonder 612. It isalso contemplated that continuous ribbon material 616 may be bonded atdifferent positions on substrates “A”-“E”, for example nearer one upperor lower edge of substrates “A”-“E”, and that the ribbon may be bondedat a different position on one or more adjacent solar substrates“A”-“E”.

FIG. 7 partially illustrates workholder 722 of indexing system 708 ofribbon bonding system 700 (in a top plan view, and a corresponding crosssectional view taken along the cross section shown in the top planview), with the top view showing substrates “A” and “B” in dashed linesand without the bonded continuous lengths of ribbon material 716 (suchas bonded portion 718 b), for ease of understanding. That is, at thebonding position of indexing system 708 (and desirably at otherlocations along indexing system 708), it is desirable to secure stringof solar substrates “A” and “B” in place during bonding. It isunderstood that there may be additional solar substrates to the left ofsubstrate “B” (relative to FIG. 7). Workholder 722 defines apertures 724along its length such that during indexing of string of solar substrates“A”-“B” walking beam members 710 may raise upwards (through apertures724) and carry string of solar substrates “A”-“B” as desired. Workholdersurface 728 (and walking beam members 710, if desired) may furtherdefine respective vacuum holes 730, 732 such that a negative fluidpressure may be drawn through one or more vacuum holes 730, 732 tosecure solar substrates (for example substrates “A”-“B”) in position.Such vacuum holes 730, 732 may be provided along the entire length ofindexing system 708, or along any portion of indexing system 708, as isdesired in a given application.

FIGS. 8A-8F are each side and corresponding top block diagram views ofvarious elements of exemplary ultrasonic ribbon bonding system 800. Theteachings of FIGS. 8A-8F may be applied to various exemplary embodimentsof the present invention, including those described above, as well asothers. At FIG. 8A, first (upper) continuous length of ribbon material816′ has already been bonded across adjacent solar substrates “A”-“B”,and second (lower) continuous length of ribbon material 816 is still inthe process of being bonded across solar substrates “A”-“B”. That is, inFIG. 8A, third bond 818 f is being formed between second (lower)continuous length of ribbon material 816 and solar substrate “B” usingbonding tool 834.

Continuous ribbon material 816 is shown being fed through ribbon guide836 adjacent bonding tool 834, such that ribbon guide 836 may beconfigured to guide the portions of the continuous length of ribbonmaterial 816 from a ribbon supply to a position proximate bonding tool834 of bond head assembly “BHA”. Ribbon guide 836 may be configured totravel along a substantially vertical axis in relation to the XY table,independent of bond head assembly “BHA”. Ribbon guide 836 may alsoinclude terminal portion 836′ proximate bonding tool 834 to limitplacement of the portions of the continuous length of the ribbonmaterial proximate bonding tool 834 within a predetermined range in a Ydirection (that is, substantially perpendicular to the direction inwhich continuous length of ribbon material follows. Ribbon guide 836 mayinclude a roller mechanism (not shown) to guide and feed continuousribbon material 816 from a spool of the ribbon material. Further, atensioner (not shown) may be positioned between the ribbon supply andribbon guide 836. The tensioner may be configured to provide apredetermined amount of tension to the portions of the continuous lengthof ribbon material 816, 816′ between the ribbon supply and thetensioner. The tensioner may also be configured to feed the portions ofthe continuous length of ribbon 816, 816′ material from the ribbonsupply through ribbon guide 836.

The detailed view of the bond head assembly “BHA” including bonding tool834 also illustrates exemplary pressing member 838 and cutter 840carried by bond head assembly “BHA” and proximate bonding tool 834.Pressing member 838 may be between cutter 840 and bonding tool 834, orcutter 840 may be between pressing member 838 and bonding tool 834.Pressing member 838 is moveable with respect to bond head assembly “BHA”independent of the bonding tool, and is configured to press againstportions 842 of the continuous length of ribbon material 816 adjacentthe formed ultrasonic bonds. When bonding tool 834 is raised abovebonded ribbon material 816 (e.g., after forming ribbon bond 818 f)pressing member 838 may secure bonded ribbon material 816 against thesurface to which it is bonded, thereby reducing the potential thatportions 842 of continuous ribbon material 816 (that may be stuck tobonding tool 834) are raised upwards with bonding tool 834 which maydamage/weaken bond 818 f and/or portions of adjacent solar substrate“B”. Pressing member 838 is moveable (independent of movement of bondingtool 834) with respect to bond head assembly “BHA”, where the bond headassembly “BHA” carries bonding tool 834 and pressing member 838. Bondhead assembly “BHA” may be configured to travel along a substantiallyvertical axis, independent of ribbon guide 836, such that bonding tool834 is adapted to form the ultrasonic bonds between the portions of thecontinuous lengths of ribbon material 816, 816′ and the plurality ofsolar substrates “A”-“C”. Further, bond head assembly “BHA” may beconfigured to rotate in an XY plane about a theta (θ) axis such thatcutter 840 may rotate about the theta (θ) axis with bond head assembly“BHA”.

After formation of third bond 818 f in second (lower) length of ribbonmaterial 816 at FIG. 8A, the string of solar substrates “A”, “B”, “C” isindexed using indexer 808 to the right such that solar substrate “C”(partially shown to the left of substrate “B” in FIG. 8A) may be movedto the bonding position on the ribbon bonder. Thus, at FIG. 8B, walkingbeam elements 810 of indexer 808 are raised together (as at arrow 844)to contact and secure (e.g., with vacuum holes that may be defined bywalking beam elements 810 such as at FIG. 7) string of solar substrates“A”-“C”. As will be appreciated by those skilled in the art, in order toindex string of solar substrates “A”-“C” the negative pressure drawnthrough the workholder through-holes may be shut off (or otherwisereleased) such that the string of solar substrates “A”-“C” may bedesirably raised above workholder surface 828 using walking beamelements 810.

At FIG. 8C, walking beam elements 810 are moved to the right (as atarrow 846). At FIG. 8D, walking beam elements 810 are lowered (as atarrow 848) such that string of solar substrates “A”-“C” are again incontact with workholder surface 828, with solar substrate “C” now in thebonding position of ultrasonic ribbon bonding system 800 (where certainribbon bonder elements, including bond head assembly “BHA”, have beenremoved from parts of FIGS. 8B-8F for simplicity), such that second(lower) continuous length of ribbon material may be bonded to solarsubstrate “C”. As will be appreciated by those skilled in the art, thenegative pressure drawn through vacuum holes of walking beam elements810 (if any) may now be shut off or otherwise released, and the negativepressure may be again drawn through workholder 822 to secure string ofsolar substrates “A”-“B” for bonding. FIG. 8E illustrates walking beamelements 810 moving to the left (as at arrow 850), below string of solarsubstrates “A”-“B” and workholder surface 828, for the next cycle ofindexing. FIG. 8F illustrates the state of string of substrates “A”-“C”(“D”) after two bonds 818 h, 818 i have been formed between lowercontinuous length of ribbon 816 and substrate “C”. Third bond 818 j ofsolar substrate “C” is in the process of being formed using bonding tool834. As shown, ribbon guide 836 is guiding continuous length of ribbon816 from a ribbon supply (e.g., a spool of continuous ribbon 815, notshown). This process may repeat as described above until the desiredlengths of continuous conductive ribbon material 816 providesinterconnection between the desired string of solar substrates, forexample “A”-“D” (with a portion of substrate “D” shown to the left ofsubstrate “C” and already having been bonded to upper continuous lengthof ribbon material 816′).

It is understood by those skilled in the art that during an ultrasonicbonding process, a transducer is used to vibrate an ultrasonic tool sothat a scrubbing motion (usually in one direction) is used to bond, forexample, a continuous length of ribbon material to a frontside and/orbackside of a substrate. During such an ultrasonic bonding process, thescrubbing motion may be: (1) substantially perpendicular to thedirection along which the continuous length of ribbon material extends;(2) substantially parallel to the direction along which the continuouslength of ribbon material extends, amongst other directions.

While the present invention is largely intended to be useful inultrasonically bonding portions of a continuous ribbon material torespective backsides of solar substrates (where the backside includes aconductive region), the present invention may also be useful in bondingribbon material to the frontside of solar substrates (where thefrontside includes active solar material configured for receiving lightenergy and converting the light energy into electrical energy).

Although the present invention has been described primarily in terms ofsolar cell bonding applications (e.g., crystalline silicon solar cells,thin film solar cells, etc.), it is not limited thereto. The teachingsof the present invention have application in any of a number ofultrasonic bonding applications (e.g., wire bonding).

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

1. An ultrasonic solar substrate bonding system comprising: a bond headassembly including a bonding tool for bonding a ribbon material to aplurality of solar substrates; a ribbon feeding system successivelysupplying portions of a continuous length of the ribbon material to thebonding tool such that the bonding tool forms ultrasonic bonds betweenthe portions of the continuous length of the ribbon material and theplurality of solar substrates; and an XY table, the bond head assemblybeing carried by the XY table, the ribbon feeding system including aribbon guide carried by the XY table, the ribbon guide being configuredto guide the portions of the continuous length of the ribbon materialfrom a ribbon supply to a position proximate the bonding tool, whereinthe bond head assembly is configured to travel along a substantiallyvertical axis, independent of the ribbon guide, such that the bondingtool is adapted to form the ultrasonic bonds between the portions of thecontinuous length of the ribbon material and the plurality of solarsubstrates.
 2. The bonding system of claim 1 wherein the plurality ofsolar substrates are crystalline solar cells.
 3. The bonding system ofclaim 1 wherein each of the plurality of solar substrates includes afrontside having exposed active solar material configured for receivinglight energy and converting the light energy into electrical energy, anda backside at least partially defined by an electrically conductiveregion.
 4. The bonding system of claim 3 wherein the bonding tool formsthe ultrasonic bonds between (1) the portions of the continuous lengthof the ribbon material, and (2) the backside of ones of the plurality ofsolar substrates.
 5. The bonding system of claim 1 further comprising analignment unit configured to position ones of the plurality of solarsubstrates in a predetermined position prior to bonding by the bondingtool.
 6. The bonding system of claim 5 further comprising a camera forimaging ones of the plurality of solar substrates prior to bonding bythe bonding tool.
 7. The bonding system of claim 6 wherein images fromthe camera are used to assist the alignment unit in positioning ones ofthe plurality of solar substrates.
 8. The bonding system of claim 1further comprising a cutter carried by the bond head assembly andproximate the bonding tool.
 9. The bonding system of claim 8 wherein thebond head assembly is configured to rotate in an XY plane about a theta(θ) axis such that the cutter rotates about the theta (θ) axis with thebond head assembly.
 10. The bonding system of claim 8 wherein thebonding tool is positioned between the cutter and the ribbon guide. 11.The bonding system of claim 8 wherein the cutter is positioned betweenthe bonding tool and the ribbon guide.
 12. The bonding system of claim 1wherein the ribbon guide includes a terminal portion proximate thebonding tool to limit placement of the portions of the continuous lengthof the ribbon material proximate the bonding tool within a predeterminedrange in a Y direction.
 13. The bonding system of claim 1 wherein theribbon guide includes a roller mechanism configured to guide and feedthe ribbon material to the bonding tool.
 14. The bonding system of claim1 wherein the ribbon supply is a spool of the ribbon material.
 15. Thebonding system of claim 1 further comprising a tensioner positionedbetween the ribbon supply and the ribbon guide, the tensioner beingconfigured to provide a predetermined amount of tension to the portionsof the continuous length of the ribbon material between the ribbonsupply and the tensioner.
 16. The bonding system of claim 15 wherein thetensioner is configured to feed the portions of the continuous length ofthe ribbon material through the ribbon guide.
 17. The bonding system ofclaim 1 further comprising a pressing member proximate the bonding tooland carried by the bond head assembly, the pressing member configured topress against the portions of the continuous length of the ribbonmaterial adjacent the ultrasonic bonds, the pressing member beingmoveable with respect to the bond head assembly independent of movementof the bonding tool.
 18. The bonding system of claim 1 furthercomprising a second bond head assembly including a second bonding tool,wherein the second bond head assembly is positioned adjacent the bondhead assembly such that respective separate lengths of the ribbonmaterial are sequentially bonded to ones of the plurality of solarsubstrates by the bonding tool and by the second bonding tool.
 19. Thebonding system of claim 18 wherein the respective separate lengths ofthe ribbon material are bonded to ones of the plurality of solarsubstrates in a substantially parallel configuration.
 20. The bondingsystem of claim 1 further comprising a material handling system forsupporting and transporting ones of the plurality of solar substrates,the ultrasonic solar substrate bonding system also comprising a secondbond head assembly including a second bonding tool, wherein the secondbond head assembly is positioned on an opposing side of the materialhandling system with respect to the bond head assembly.
 21. The bondingsystem of claim 20 wherein the bonding tool and the second bonding toolare configured to bond respective separate lengths of the ribbonmaterial to ones of the plurality of solar substrates.
 22. The bondingsystem of claim 20 wherein the respective separate lengths of the ribbonmaterial are bonded to ones of the plurality of solar substrates in asubstantially parallel configuration.
 23. The bonding system of claim 20further comprising a material handling system configured to: (a) supportones of the plurality of solar substrates upstream of the bond headassembly; (b) position the ones of the plurality of solar substratesunder the bond head assembly for bonding by the bond head assembly; and(c) support bonded ones of the plurality of solar substrates downstreamof the bond head assembly.
 24. The bonding system of claim 23 whereinthe material handling system comprises a walking beam structureconfigured to move the ones of the plurality of solar substrates withrespect to the bond head assembly, and a workholder structure configuredto support the ones of the plurality of solar substrates during a ribbonbonding operation.
 25. The bonding system of claim 24 wherein at leastone of the walking beam structure and the workholder structure includesa plurality of through-holes.
 26. The bonding system of claim 25 whereina negative fluid pressure is drawn through the plurality ofthrough-holes to retain the ones of the plurality of solar substrates ina position along the material handling system.